The present invention relates to lighting and more particularly to a lamp assembly for use in connection with inductively powered lighting.
Although not widely available, inductively coupled lighting systems are known. A conventional inductively coupled lighting system generally includes a primary circuit having a primary coil (or “primary”) that is driven by a power supply and a secondary circuit having a secondary coil (or “secondary”) that inductively receives power from the primary. Inductive couplings provide a number of advantages over conventional direct electrical connections. First, inductively coupled lamps are typically safer and easier to connect and disconnect than hardwired lamps. With direct electrical connections, it is generally necessary to manipulate electrical connectors when installing and removing the inductively powered lamp assembly. This typically requires some effort and creates a risk of electrical shock. Often, the electrical connectors are at least partially exposed, thereby increasing the risk of electrical shock. Inductively coupled lamps, on the other hand, do not require the manipulation of any electrical connectors. Instead, the secondary of the inductively powered lamp assembly simply needs to be placed adjacent to the primary to permit the supply of power to the inductively powered lamp assembly. Second, the elimination of electrical connectors also increases the reliability of the system by eliminating the problems associated with conventional electrical connectors. For example, conventional electrical connectors are subject to corrosion and to wear. These problems are particularly acute in an outdoor setting where environmental conditions may subject the electrical connectors to moisture. With repeated use, mechanical connectors are also subject to wear and eventual failure. Third, inductively coupled lamps inherently provide a lower risk of an electrical hazard at the inductively powered lamp assembly. As noted above, the inductively powered lamp assembly is electrically separated from the power source. All power must be inductively passed from the power source to the inductively powered lamp assembly. Because there is an intrinsic limit on the amount of power that can be inductively passed to the inductively powered lamp assembly, the amount of power at the inductively powered lamp assembly is limited and the risk of electrical hazards is reduced.
Although conventional inductively coupled lamps provide a number of important advantages over directly connected lamps, they do suffer significant drawbacks. An inductive coupling is inherently less efficient than a direct electrical connector. This is partly due to the power required to create and sustain the electromagnetic field. The primary inefficiencies in a conventional inductive coupling result from a poorly tuned circuit. These inefficiencies are manifest in increased heat gain and in noise created by vibration in the primary and secondary. The efficiency issues are exaggerated with higher power lighting applications. In addition, existing lamp circuits require precise alignment of the primary and secondary to provide any reasonable level of efficiency. This requires more precise tolerances and limits the configuration and layout of the inductively powered lamp assembly and the overall lamp.
One of the largest reliability issues facing the lamp industry is caused by the penetration of the lamp sleeve by wires or other electrical conductors. Typically, the wires pass into the interior of the lamp through a glass stem. Because glass does not readily adhere to and seal around the wires, there is a material risk of lamp leakage at the point the wires penetrate the lamp. Although efforts have been made to optimize the seal, this remains a significant reliability concern.
With conventional inductively powered lamps, there is also reliability issues associated with exposure of the lamp circuit components to the environment, for example, water and moisture from the environment can damage circuit components. To address this concern, at least one inductively powered lighting system encloses the entire lamp assembly within a sealed enclosure. U.S. Pat. No. 5,264,997 to Hutchisson et al discloses a lamp that is mounted to a printed wiring board that is spaced from the secondary on a plurality of posts. The printed wiring board includes various electrical component required for operation of the inductive coupling. Separate shell and lens components are sealed together to form a leak tight enclosure around the lamp, the printed wiring board and the secondary. The shell is specially shaped to receive the secondary and to be interfitted with a socket containing the primary. Although the sealed enclosure provides improved protection from environmental conditions, it is relatively bulky and only provides light transmission in the direction of the lens.
As can be seen, there remains a need for an inductively coupled lamp assembly that is efficient, provides improved reliability in a variety of conditions and is easily adapted to many different lamp configurations.